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<a href="async_2util_8hpp.html">Go to the documentation of this file.</a><div class="fragment"><div class="line"><a id="l00001" name="l00001"></a><span class="lineno">    1</span><span class="comment">/* Flow</span></div>
<div class="line"><a id="l00002" name="l00002"></a><span class="lineno">    2</span><span class="comment"> * Copyright 2023 Akamai Technologies, Inc.</span></div>
<div class="line"><a id="l00003" name="l00003"></a><span class="lineno">    3</span><span class="comment"> *</span></div>
<div class="line"><a id="l00004" name="l00004"></a><span class="lineno">    4</span><span class="comment"> * Licensed under the Apache License, Version 2.0 (the</span></div>
<div class="line"><a id="l00005" name="l00005"></a><span class="lineno">    5</span><span class="comment"> * &quot;License&quot;); you may not use this file except in</span></div>
<div class="line"><a id="l00006" name="l00006"></a><span class="lineno">    6</span><span class="comment"> * compliance with the License.  You may obtain a copy</span></div>
<div class="line"><a id="l00007" name="l00007"></a><span class="lineno">    7</span><span class="comment"> * of the License at</span></div>
<div class="line"><a id="l00008" name="l00008"></a><span class="lineno">    8</span><span class="comment"> *</span></div>
<div class="line"><a id="l00009" name="l00009"></a><span class="lineno">    9</span><span class="comment"> *   https://www.apache.org/licenses/LICENSE-2.0</span></div>
<div class="line"><a id="l00010" name="l00010"></a><span class="lineno">   10</span><span class="comment"> *</span></div>
<div class="line"><a id="l00011" name="l00011"></a><span class="lineno">   11</span><span class="comment"> * Unless required by applicable law or agreed to in</span></div>
<div class="line"><a id="l00012" name="l00012"></a><span class="lineno">   12</span><span class="comment"> * writing, software distributed under the License is</span></div>
<div class="line"><a id="l00013" name="l00013"></a><span class="lineno">   13</span><span class="comment"> * distributed on an &quot;AS IS&quot; BASIS, WITHOUT WARRANTIES OR</span></div>
<div class="line"><a id="l00014" name="l00014"></a><span class="lineno">   14</span><span class="comment"> * CONDITIONS OF ANY KIND, either express or implied.</span></div>
<div class="line"><a id="l00015" name="l00015"></a><span class="lineno">   15</span><span class="comment"> * See the License for the specific language governing</span></div>
<div class="line"><a id="l00016" name="l00016"></a><span class="lineno">   16</span><span class="comment"> * permissions and limitations under the License. */</span></div>
<div class="line"><a id="l00017" name="l00017"></a><span class="lineno">   17</span><span class="comment"></span> </div>
<div class="line"><a id="l00018" name="l00018"></a><span class="lineno">   18</span><span class="comment">/// @file</span></div>
<div class="line"><a id="l00019" name="l00019"></a><span class="lineno">   19</span><span class="comment"></span><span class="preprocessor">#pragma once</span></div>
<div class="line"><a id="l00020" name="l00020"></a><span class="lineno">   20</span> </div>
<div class="line"><a id="l00021" name="l00021"></a><span class="lineno">   21</span><span class="preprocessor">#include &quot;<a class="code" href="async__fwd_8hpp.html">flow/async/async_fwd.hpp</a>&quot;</span></div>
<div class="line"><a id="l00022" name="l00022"></a><span class="lineno">   22</span> </div>
<div class="line"><a id="l00023" name="l00023"></a><span class="lineno">   23</span><span class="keyword">namespace </span><a class="code hl_namespace" href="namespaceflow_1_1async.html">flow::async</a></div>
<div class="line"><a id="l00024" name="l00024"></a><span class="lineno">   24</span>{</div>
<div class="line"><a id="l00025" name="l00025"></a><span class="lineno">   25</span> </div>
<div class="line"><a id="l00026" name="l00026"></a><span class="lineno">   26</span><span class="comment">// Free functions: in *_fwd.hpp.</span></div>
<div class="line"><a id="l00027" name="l00027"></a><span class="lineno">   27</span> </div>
<div class="line"><a id="l00028" name="l00028"></a><span class="lineno">   28</span><span class="comment">// Template implementations.</span></div>
<div class="line"><a id="l00029" name="l00029"></a><span class="lineno">   29</span> </div>
<div class="line"><a id="l00030" name="l00030"></a><span class="lineno">   30</span><span class="keyword">template</span>&lt;<span class="keyword">typename</span> Execution_context&gt;</div>
<div class="line"><a id="l00031" name="l00031"></a><span class="lineno"><a class="line" href="namespaceflow_1_1async.html#a24567271e97a67d3cae6bd8bf8dc63c4">   31</a></span><span class="keywordtype">void</span> <a class="code hl_function" href="namespaceflow_1_1async.html#a24567271e97a67d3cae6bd8bf8dc63c4">asio_exec_ctx_post</a>(<a class="code hl_class" href="classflow_1_1log_1_1Logger.html">log::Logger</a>* logger_ptr, Execution_context* exec_ctx, <a class="code hl_enumeration" href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485">Synchronicity</a> synchronicity, <a class="code hl_class" href="classflow_1_1Function.html">Task</a>&amp;&amp; task)</div>
<div class="line"><a id="l00032" name="l00032"></a><span class="lineno">   32</span>{</div>
<div class="line"><a id="l00033" name="l00033"></a><span class="lineno">   33</span>  <span class="keyword">using </span><a class="code hl_enumeration" href="namespaceflow_1_1log.html#a5c602384e6fe9d7642740ac2fae4ad04">log::Sev</a>;</div>
<div class="line"><a id="l00034" name="l00034"></a><span class="lineno">   34</span>  <span class="keyword">using </span>boost::asio::post;</div>
<div class="line"><a id="l00035" name="l00035"></a><span class="lineno">   35</span>  <span class="keyword">using </span>boost::asio::dispatch;</div>
<div class="line"><a id="l00036" name="l00036"></a><span class="lineno">   36</span>  <span class="keyword">using </span>boost::promise;</div>
<div class="line"><a id="l00037" name="l00037"></a><span class="lineno">   37</span> </div>
<div class="line"><a id="l00038" name="l00038"></a><span class="lineno">   38</span>  <a class="code hl_define" href="log_8hpp.html#ae4b5d4fdd2eb052615620879dd74af95">FLOW_LOG_SET_CONTEXT</a>(logger_ptr, Flow_log_component::S_ASYNC);</div>
<div class="line"><a id="l00039" name="l00039"></a><span class="lineno">   39</span> </div>
<div class="line"><a id="l00040" name="l00040"></a><span class="lineno">   40</span>  <span class="comment">/* As noted in contract, Execution_context is either Task_engine or Strand.  Since a Strand is born of a Task_engine,</span></div>
<div class="line"><a id="l00041" name="l00041"></a><span class="lineno">   41</span><span class="comment">   * everything that would apply to its parent Task_engine applies to the Strand, so we can talk about exclusively</span></div>
<div class="line"><a id="l00042" name="l00042"></a><span class="lineno">   42</span><span class="comment">   * Task_engines in below comments to explain the reasoning.  Strand only adds an extra constraint, namely that</span></div>
<div class="line"><a id="l00043" name="l00043"></a><span class="lineno">   43</span><span class="comment">   * the chosen thread is not executing something from the same Strand at the time that F() eventually runs.  This is</span></div>
<div class="line"><a id="l00044" name="l00044"></a><span class="lineno">   44</span><span class="comment">   * typically irrelevant to the below logic; when it is relevant we will explicitly discuss the possibility that</span></div>
<div class="line"><a id="l00045" name="l00045"></a><span class="lineno">   45</span><span class="comment">   * *exec_ctx is a Strand after all.</span></div>
<div class="line"><a id="l00046" name="l00046"></a><span class="lineno">   46</span><span class="comment">   *</span></div>
<div class="line"><a id="l00047" name="l00047"></a><span class="lineno">   47</span><span class="comment">   * Lastly, as the contract notes, this all quite likely works with the general ExecutionContext formal concept</span></div>
<div class="line"><a id="l00048" name="l00048"></a><span class="lineno">   48</span><span class="comment">   * from boost.asio docs; but we have made no formal effort to ensure this in our comments/reasoning.  This may be</span></div>
<div class="line"><a id="l00049" name="l00049"></a><span class="lineno">   49</span><span class="comment">   * corrected as needed in the future.</span></div>
<div class="line"><a id="l00050" name="l00050"></a><span class="lineno">   50</span><span class="comment">   *</span></div>
<div class="line"><a id="l00051" name="l00051"></a><span class="lineno">   51</span><span class="comment">   * Let us now discuss the asio_exec_ctx_post(E, synchronicity, F) call, where E is a Task_engine.</span></div>
<div class="line"><a id="l00052" name="l00052"></a><span class="lineno">   52</span><span class="comment">   *</span></div>
<div class="line"><a id="l00053" name="l00053"></a><span class="lineno">   53</span><span class="comment">   * We post to some random-ish thread in E, which is run()ning in at least 1 thread, using built-in Task_engine</span></div>
<div class="line"><a id="l00054" name="l00054"></a><span class="lineno">   54</span><span class="comment">   * (boost.asio) functionality wherein: post(E, F) will execute F() within any thread currently executing E.run(),</span></div>
<div class="line"><a id="l00055" name="l00055"></a><span class="lineno">   55</span><span class="comment">   * for a given Task_engine E.</span></div>
<div class="line"><a id="l00056" name="l00056"></a><span class="lineno">   56</span><span class="comment">   *</span></div>
<div class="line"><a id="l00057" name="l00057"></a><span class="lineno">   57</span><span class="comment">   * post(E, F) is indeed used in the most common synchronicity mode, S_ASYNC, and in its</span></div>
<div class="line"><a id="l00058" name="l00058"></a><span class="lineno">   58</span><span class="comment">   * close cousin S_ASYNC_AND_AWAIT_CONCURRENT_COMPLETION.  If calling thread is outside pool E, then</span></div>
<div class="line"><a id="l00059" name="l00059"></a><span class="lineno">   59</span><span class="comment">   * F() will run sometime in the future concurrently to the calling thread; including to our code in this method.</span></div>
<div class="line"><a id="l00060" name="l00060"></a><span class="lineno">   60</span><span class="comment">   * If calling thread is in E&#39;s pool (we&#39;re in in a task being called by E.run() now), then F()</span></div>
<div class="line"><a id="l00061" name="l00061"></a><span class="lineno">   61</span><span class="comment">   * will run sometime after we return.</span></div>
<div class="line"><a id="l00062" name="l00062"></a><span class="lineno">   62</span><span class="comment">   *</span></div>
<div class="line"><a id="l00063" name="l00063"></a><span class="lineno">   63</span><span class="comment">   * However, S_ASYNC_AND_AWAIT_CONCURRENT_COMPLETION will additionally cause us to await F()&#39;s completion before</span></div>
<div class="line"><a id="l00064" name="l00064"></a><span class="lineno">   64</span><span class="comment">   * we return control to caller.  If we&#39;re inside pool E, this might cause a deadlock (and *definitely* will</span></div>
<div class="line"><a id="l00065" name="l00065"></a><span class="lineno">   65</span><span class="comment">   * if n_threads() == 1), because we&#39;ll wait to return &#39;til a condition that can only become true after we return</span></div>
<div class="line"><a id="l00066" name="l00066"></a><span class="lineno">   66</span><span class="comment">   * (unless by luck the post() targets a different thread in the pool).  Hence we advertise undefined behavior if the</span></div>
<div class="line"><a id="l00067" name="l00067"></a><span class="lineno">   67</span><span class="comment">   * user makes the improper choice to use this mode from inside an E-posted task.</span></div>
<div class="line"><a id="l00068" name="l00068"></a><span class="lineno">   68</span><span class="comment">   *</span></div>
<div class="line"><a id="l00069" name="l00069"></a><span class="lineno">   69</span><span class="comment">   * [Sanity check: What if E is a Strand after all (from some Task_engine E*), and F() is currently executing from</span></div>
<div class="line"><a id="l00070" name="l00070"></a><span class="lineno">   70</span><span class="comment">   * within E*&#39;s pool after all... but also E* happens to have itself been posted through some *other* Strand</span></div>
<div class="line"><a id="l00071" name="l00071"></a><span class="lineno">   71</span><span class="comment">   * E#?  Would that preclude the deadlock situation, since seemingly being in different Strands would prevent</span></div>
<div class="line"><a id="l00072" name="l00072"></a><span class="lineno">   72</span><span class="comment">   * boost.asio from posting F() onto W (current thread)?  Answer: No; just because it can&#39;t put it on the current</span></div>
<div class="line"><a id="l00073" name="l00073"></a><span class="lineno">   73</span><span class="comment">   * thread *now* doesn&#39;t mean it can&#39;t queue it to run on W after we return... and we&#39;re back to deadlock.  So,</span></div>
<div class="line"><a id="l00074" name="l00074"></a><span class="lineno">   74</span><span class="comment">   * the contract stands without any further allowances due to E&#39;s Strandiness.]</span></div>
<div class="line"><a id="l00075" name="l00075"></a><span class="lineno">   75</span><span class="comment">   *</span></div>
<div class="line"><a id="l00076" name="l00076"></a><span class="lineno">   76</span><span class="comment">   * S_ASYNC_AND_AWAIT_CONCURRENT_START is similar to ..._COMPLETION; but it returns &quot;early&quot;: just before F()</span></div>
<div class="line"><a id="l00077" name="l00077"></a><span class="lineno">   77</span><span class="comment">   * executes (in such a way as to guarantee E.stop(), when E is a Task_engine, executed after we return will be unable</span></div>
<div class="line"><a id="l00078" name="l00078"></a><span class="lineno">   78</span><span class="comment">   * to prevent F() from running).  The same deadlock situation applies: we can&#39;t wait for F() to start, if it can only</span></div>
<div class="line"><a id="l00079" name="l00079"></a><span class="lineno">   79</span><span class="comment">   * start once we&#39;re done waiting.</span></div>
<div class="line"><a id="l00080" name="l00080"></a><span class="lineno">   80</span><span class="comment">   *</span></div>
<div class="line"><a id="l00081" name="l00081"></a><span class="lineno">   81</span><span class="comment">   * Lastly: S_OPPORTUNISTIC_SYNC_ELSE_ASYNC is much like S_ASYNC, except dispatch(E, F) is used instead of post(E, F).</span></div>
<div class="line"><a id="l00082" name="l00082"></a><span class="lineno">   82</span><span class="comment">   * If post(E, F) would have caused F() to execute in the current thread anyway as soon as we return, then F() is</span></div>
<div class="line"><a id="l00083" name="l00083"></a><span class="lineno">   83</span><span class="comment">   * executed synchronously, now, and *then* we will return.  (This is a performance shortcut, so that boost.asio</span></div>
<div class="line"><a id="l00084" name="l00084"></a><span class="lineno">   84</span><span class="comment">   * won&#39;t pointlessly exit us and immediately re-enter F().)  If, however, post(E, F) would have caused F() to execute</span></div>
<div class="line"><a id="l00085" name="l00085"></a><span class="lineno">   85</span><span class="comment">   * on some other thread and/or later, then dispatch(E, F) acts identically to post(E, F) after all, meaning it&#39;ll</span></div>
<div class="line"><a id="l00086" name="l00086"></a><span class="lineno">   86</span><span class="comment">   * execute in the background concurrently and/or later.  (In other words, the performance shortcut is not possible</span></div>
<div class="line"><a id="l00087" name="l00087"></a><span class="lineno">   87</span><span class="comment">   * due to other constraints.) */</span></div>
<div class="line"><a id="l00088" name="l00088"></a><span class="lineno">   88</span> </div>
<div class="line"><a id="l00089" name="l00089"></a><span class="lineno">   89</span>  <span class="comment">// @todo Maybe provide operator&lt;&lt;(ostream, Task_engine/Strand) so we can output *exec_ctx too.</span></div>
<div class="line"><a id="l00090" name="l00090"></a><span class="lineno">   90</span>  <a class="code hl_define" href="log_8hpp.html#affcf2e4c496ce3f42adf981669c623b8">FLOW_LOG_TRACE</a>(<span class="stringliteral">&quot;About to post task via boost.asio execution context (Task_engine or Strand as of this writing) &quot;</span></div>
<div class="line"><a id="l00091" name="l00091"></a><span class="lineno">   91</span>                 <span class="stringliteral">&quot;[@&quot;</span> &lt;&lt; exec_ctx &lt;&lt; <span class="stringliteral">&quot;]; might sync-execute in this thread? = &quot;</span></div>
<div class="line"><a id="l00092" name="l00092"></a><span class="lineno">   92</span>                 <span class="stringliteral">&quot;[&quot;</span> &lt;&lt; (synchronicity == <a class="code hl_enumvalue" href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485aff6bc53ee6c14f2eee463c06d9dff01f">Synchronicity::S_OPPORTUNISTIC_SYNC_ELSE_ASYNC</a>) &lt;&lt; <span class="stringliteral">&quot;]; &quot;</span></div>
<div class="line"><a id="l00093" name="l00093"></a><span class="lineno">   93</span>                 <span class="stringliteral">&quot;will we ensure concurrent completion before continuing? = &quot;</span></div>
<div class="line"><a id="l00094" name="l00094"></a><span class="lineno">   94</span>                 <span class="stringliteral">&quot;[&quot;</span> &lt;&lt; (synchronicity == <a class="code hl_enumvalue" href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485a57525f29ac96f4edd56c951e7d7c7b25">Synchronicity::S_ASYNC_AND_AWAIT_CONCURRENT_COMPLETION</a>) &lt;&lt; <span class="stringliteral">&quot;]; &quot;</span></div>
<div class="line"><a id="l00095" name="l00095"></a><span class="lineno">   95</span>                 <span class="stringliteral">&quot;will we ensure concurrent initiation before continuing? = &quot;</span></div>
<div class="line"><a id="l00096" name="l00096"></a><span class="lineno">   96</span>                 <span class="stringliteral">&quot;[&quot;</span> &lt;&lt; (synchronicity == <a class="code hl_enumvalue" href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485ae9a9ae292ea3fbbe3b313348dcec0846">Synchronicity::S_ASYNC_AND_AWAIT_CONCURRENT_START</a>) &lt;&lt; <span class="stringliteral">&quot;].&quot;</span>);</div>
<div class="line"><a id="l00097" name="l00097"></a><span class="lineno">   97</span> </div>
<div class="line"><a id="l00098" name="l00098"></a><span class="lineno">   98</span>  <a class="code hl_class" href="classflow_1_1Function.html">Task</a> actual_task(std::move(task));</div>
<div class="line"><a id="l00099" name="l00099"></a><span class="lineno">   99</span> </div>
<div class="line"><a id="l00100" name="l00100"></a><span class="lineno">  100</span>  <span class="comment">/* If the current log level suggests we want TRACE logging then book-end their task with some log statements.</span></div>
<div class="line"><a id="l00101" name="l00101"></a><span class="lineno">  101</span><span class="comment">   * For perf: entirely avoid this wrapping if almost certainly no logging would occur anyway. */</span></div>
<div class="line"><a id="l00102" name="l00102"></a><span class="lineno">  102</span>  <span class="keywordflow">if</span> (logger_ptr &amp;&amp; logger_ptr-&gt;<a class="code hl_function" href="classflow_1_1log_1_1Logger.html#ac8a2e7a33fe3fbc0c29ead62ed98c022">should_log</a>(Sev::S_TRACE, get_log_component()))</div>
<div class="line"><a id="l00103" name="l00103"></a><span class="lineno">  103</span>  {</div>
<div class="line"><a id="l00104" name="l00104"></a><span class="lineno">  104</span>    actual_task = [get_logger, get_log_component, wrapped_task = std::move(actual_task)]()</div>
<div class="line"><a id="l00105" name="l00105"></a><span class="lineno">  105</span>    {</div>
<div class="line"><a id="l00106" name="l00106"></a><span class="lineno">  106</span>      <a class="code hl_define" href="log_8hpp.html#affcf2e4c496ce3f42adf981669c623b8">FLOW_LOG_TRACE</a>(<span class="stringliteral">&quot;Task starting: current processor logical core index [&quot;</span> &lt;&lt; <a class="code hl_function" href="namespaceflow_1_1async.html#a4cce43f39672e80cba5512103c53ae60">cpu_idx</a>() &lt;&lt; <span class="stringliteral">&quot;].&quot;</span>);</div>
<div class="line"><a id="l00107" name="l00107"></a><span class="lineno">  107</span>      wrapped_task();</div>
<div class="line"><a id="l00108" name="l00108"></a><span class="lineno">  108</span>      <a class="code hl_define" href="log_8hpp.html#affcf2e4c496ce3f42adf981669c623b8">FLOW_LOG_TRACE</a>(<span class="stringliteral">&quot;Task ended: current processor logical core index [&quot;</span> &lt;&lt; <a class="code hl_function" href="namespaceflow_1_1async.html#a4cce43f39672e80cba5512103c53ae60">cpu_idx</a>() &lt;&lt; <span class="stringliteral">&quot;].&quot;</span>);</div>
<div class="line"><a id="l00109" name="l00109"></a><span class="lineno">  109</span>    };</div>
<div class="line"><a id="l00110" name="l00110"></a><span class="lineno">  110</span>  }</div>
<div class="line"><a id="l00111" name="l00111"></a><span class="lineno">  111</span> </div>
<div class="line"><a id="l00112" name="l00112"></a><span class="lineno">  112</span>  <span class="comment">/* Now we want to (1) post `actual_task` onto *m_shared_task_engine, so that it runs at some point; and (2)</span></div>
<div class="line"><a id="l00113" name="l00113"></a><span class="lineno">  113</span><span class="comment">   * either wait or not wait for it to complete concurrently.  The details are discussed above and</span></div>
<div class="line"><a id="l00114" name="l00114"></a><span class="lineno">  114</span><span class="comment">   * in Synchronicity member doc headers. */</span></div>
<div class="line"><a id="l00115" name="l00115"></a><span class="lineno">  115</span> </div>
<div class="line"><a id="l00116" name="l00116"></a><span class="lineno">  116</span>  <span class="keywordflow">if</span> (synchronicity == <a class="code hl_enumvalue" href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485a4d7a5700444c0570af37b1f9bcc6eb1f">Synchronicity::S_ASYNC</a>)</div>
<div class="line"><a id="l00117" name="l00117"></a><span class="lineno">  117</span>  {</div>
<div class="line"><a id="l00118" name="l00118"></a><span class="lineno">  118</span>    post(*exec_ctx, std::move(actual_task));</div>
<div class="line"><a id="l00119" name="l00119"></a><span class="lineno">  119</span>    <span class="comment">// That&#39;s it; give control back to caller.  actual_task() has not run here (but may run concurrently).</span></div>
<div class="line"><a id="l00120" name="l00120"></a><span class="lineno">  120</span>  }</div>
<div class="line"><a id="l00121" name="l00121"></a><span class="lineno">  121</span>  <span class="keywordflow">else</span> <span class="keywordflow">if</span> (synchronicity == <a class="code hl_enumvalue" href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485aff6bc53ee6c14f2eee463c06d9dff01f">Synchronicity::S_OPPORTUNISTIC_SYNC_ELSE_ASYNC</a>)</div>
<div class="line"><a id="l00122" name="l00122"></a><span class="lineno">  122</span>  {</div>
<div class="line"><a id="l00123" name="l00123"></a><span class="lineno">  123</span>    dispatch(*exec_ctx, std::move(actual_task));</div>
<div class="line"><a id="l00124" name="l00124"></a><span class="lineno">  124</span>    <span class="comment">// That&#39;s it; give control back to caller.  actual_task() may have just run -- or else it&#39;s just like post().</span></div>
<div class="line"><a id="l00125" name="l00125"></a><span class="lineno">  125</span>  }</div>
<div class="line"><a id="l00126" name="l00126"></a><span class="lineno">  126</span>  <span class="keywordflow">else</span></div>
<div class="line"><a id="l00127" name="l00127"></a><span class="lineno">  127</span>  {</div>
<div class="line"><a id="l00128" name="l00128"></a><span class="lineno">  128</span>    <span class="keyword">const</span> <span class="keywordtype">bool</span> assure_finish_else_start = synchronicity == <a class="code hl_enumvalue" href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485a57525f29ac96f4edd56c951e7d7c7b25">Synchronicity::S_ASYNC_AND_AWAIT_CONCURRENT_COMPLETION</a>;</div>
<div class="line"><a id="l00129" name="l00129"></a><span class="lineno">  129</span>    assert((assure_finish_else_start || (synchronicity == <a class="code hl_enumvalue" href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485ae9a9ae292ea3fbbe3b313348dcec0846">Synchronicity::S_ASYNC_AND_AWAIT_CONCURRENT_START</a>))</div>
<div class="line"><a id="l00130" name="l00130"></a><span class="lineno">  130</span>           &amp;&amp; <span class="stringliteral">&quot;asio_exec_ctx_post() failed to handle one of the Synchronicity enum values.&quot;</span>);</div>
<div class="line"><a id="l00131" name="l00131"></a><span class="lineno">  131</span> </div>
<div class="line"><a id="l00132" name="l00132"></a><span class="lineno">  132</span>    <span class="comment">/* In this interesting mode, by contract, we are *not* in W now.  (@todo Consider finding a way to assert() this.)</span></div>
<div class="line"><a id="l00133" name="l00133"></a><span class="lineno">  133</span><span class="comment">     * As noted above we still post(E, F) -- but instead of returning await its completion, or initiation; then return.</span></div>
<div class="line"><a id="l00134" name="l00134"></a><span class="lineno">  134</span><span class="comment">     * A future/promise pair accomplishes the latter easily.  (Historical note: I (ygoldfel) used to do the</span></div>
<div class="line"><a id="l00135" name="l00135"></a><span class="lineno">  135</span><span class="comment">     * future/promise thing manually in many places.  It&#39;s boiler-plate, short but a little hairy, so it&#39;s nice to</span></div>
<div class="line"><a id="l00136" name="l00136"></a><span class="lineno">  136</span><span class="comment">     * give them this feature instead.  Also some might not know about promise/future and try to use</span></div>
<div class="line"><a id="l00137" name="l00137"></a><span class="lineno">  137</span><span class="comment">     * mutex/cond_var, which is always a nightmare of potential bugs.) */</span></div>
<div class="line"><a id="l00138" name="l00138"></a><span class="lineno">  138</span> </div>
<div class="line"><a id="l00139" name="l00139"></a><span class="lineno">  139</span>    <a class="code hl_define" href="log_8hpp.html#affcf2e4c496ce3f42adf981669c623b8">FLOW_LOG_TRACE</a>(<span class="stringliteral">&quot;From outside thread pool, we post task to execute concurrently; and await its &quot;</span></div>
<div class="line"><a id="l00140" name="l00140"></a><span class="lineno">  140</span>                   <span class="stringliteral">&quot;[&quot;</span> &lt;&lt; (assure_finish_else_start ? <span class="stringliteral">&quot;completion&quot;</span> : <span class="stringliteral">&quot;initiation&quot;</span>) &lt;&lt; <span class="stringliteral">&quot;].  &quot;</span></div>
<div class="line"><a id="l00141" name="l00141"></a><span class="lineno">  141</span>                   <span class="stringliteral">&quot;A deadlock here implies bug, namely that we are *not* outside thread pool now after all.&quot;</span>);</div>
<div class="line"><a id="l00142" name="l00142"></a><span class="lineno">  142</span> </div>
<div class="line"><a id="l00143" name="l00143"></a><span class="lineno">  143</span>    promise&lt;void&gt; wait_done_promise;</div>
<div class="line"><a id="l00144" name="l00144"></a><span class="lineno">  144</span> </div>
<div class="line"><a id="l00145" name="l00145"></a><span class="lineno">  145</span>    <span class="keywordflow">if</span> (assure_finish_else_start)</div>
<div class="line"><a id="l00146" name="l00146"></a><span class="lineno">  146</span>    {</div>
<div class="line"><a id="l00147" name="l00147"></a><span class="lineno">  147</span>      post(*exec_ctx, [&amp;]() <span class="comment">// We&#39;re gonna block until the task completes, so just keep all context by &amp;reference.</span></div>
<div class="line"><a id="l00148" name="l00148"></a><span class="lineno">  148</span>      {</div>
<div class="line"><a id="l00149" name="l00149"></a><span class="lineno">  149</span>        actual_task();</div>
<div class="line"><a id="l00150" name="l00150"></a><span class="lineno">  150</span>        wait_done_promise.set_value();</div>
<div class="line"><a id="l00151" name="l00151"></a><span class="lineno">  151</span>      });</div>
<div class="line"><a id="l00152" name="l00152"></a><span class="lineno">  152</span>    }</div>
<div class="line"><a id="l00153" name="l00153"></a><span class="lineno">  153</span>    <span class="keywordflow">else</span></div>
<div class="line"><a id="l00154" name="l00154"></a><span class="lineno">  154</span>    {</div>
<div class="line"><a id="l00155" name="l00155"></a><span class="lineno">  155</span>      post(*exec_ctx, [&amp;wait_done_promise, <span class="comment">// Safe to capture: .get_future().wait() returns after .set_value().</span></div>
<div class="line"><a id="l00156" name="l00156"></a><span class="lineno">  156</span>                       actual_task = std::move(actual_task)] <span class="comment">// Gotta cap it; else `actual_task` hosed while executing.</span></div>
<div class="line"><a id="l00157" name="l00157"></a><span class="lineno">  157</span>                        ()</div>
<div class="line"><a id="l00158" name="l00158"></a><span class="lineno">  158</span>      {</div>
<div class="line"><a id="l00159" name="l00159"></a><span class="lineno">  159</span>        wait_done_promise.set_value(); <span class="comment">// We&#39;ve started!  Nothing (other than a thread killing) can prevent:</span></div>
<div class="line"><a id="l00160" name="l00160"></a><span class="lineno">  160</span>        actual_task();</div>
<div class="line"><a id="l00161" name="l00161"></a><span class="lineno">  161</span>      });</div>
<div class="line"><a id="l00162" name="l00162"></a><span class="lineno">  162</span>    }</div>
<div class="line"><a id="l00163" name="l00163"></a><span class="lineno">  163</span> </div>
<div class="line"><a id="l00164" name="l00164"></a><span class="lineno">  164</span>    wait_done_promise.get_future().wait();</div>
<div class="line"><a id="l00165" name="l00165"></a><span class="lineno">  165</span>    <a class="code hl_define" href="log_8hpp.html#affcf2e4c496ce3f42adf981669c623b8">FLOW_LOG_TRACE</a>(<span class="stringliteral">&quot;Wait for concurrent execution complete.  Done.&quot;</span>);</div>
<div class="line"><a id="l00166" name="l00166"></a><span class="lineno">  166</span> </div>
<div class="line"><a id="l00167" name="l00167"></a><span class="lineno">  167</span>    <span class="comment">/* That&#39;s it; give control back to caller.  actual_task() *did* run and finish but not in here; or at least</span></div>
<div class="line"><a id="l00168" name="l00168"></a><span class="lineno">  168</span><span class="comment">     * it will have definitely finished eventually, even if caller tries E.stop() (if applicable) after we return. */</span></div>
<div class="line"><a id="l00169" name="l00169"></a><span class="lineno">  169</span>  } <span class="comment">// if (sync == S_ASYNC_AND_AWAIT_CONCURRENT_{COMPLETION|START})</span></div>
<div class="line"><a id="l00170" name="l00170"></a><span class="lineno">  170</span>} <span class="comment">// asio_exec_ctx_post()</span></div>
<div class="line"><a id="l00171" name="l00171"></a><span class="lineno">  171</span> </div>
<div class="line"><a id="l00172" name="l00172"></a><span class="lineno">  172</span>} <span class="comment">// namespace flow::async</span></div>
<div class="ttc" id="aasync__fwd_8hpp_html"><div class="ttname"><a href="async__fwd_8hpp.html">async_fwd.hpp</a></div></div>
<div class="ttc" id="aclassflow_1_1Function_html"><div class="ttname"><a href="classflow_1_1Function.html">flow::Function</a></div><div class="ttdef"><b>Definition:</b> <a href="common_8hpp_source.html#l00512">common.hpp:512</a></div></div>
<div class="ttc" id="aclassflow_1_1log_1_1Logger_html"><div class="ttname"><a href="classflow_1_1log_1_1Logger.html">flow::log::Logger</a></div><div class="ttdoc">Interface that the user should implement, passing the implementing Logger into logging classes (Flow'...</div><div class="ttdef"><b>Definition:</b> <a href="log_8hpp_source.html#l01280">log.hpp:1284</a></div></div>
<div class="ttc" id="aclassflow_1_1log_1_1Logger_html_ac8a2e7a33fe3fbc0c29ead62ed98c022"><div class="ttname"><a href="classflow_1_1log_1_1Logger.html#ac8a2e7a33fe3fbc0c29ead62ed98c022">flow::log::Logger::should_log</a></div><div class="ttdeci">virtual bool should_log(Sev sev, const Component &amp;component) const =0</div><div class="ttdoc">Given attributes of a hypothetical message that would be logged, return true if that message should b...</div></div>
<div class="ttc" id="alog_8hpp_html_ae4b5d4fdd2eb052615620879dd74af95"><div class="ttname"><a href="log_8hpp.html#ae4b5d4fdd2eb052615620879dd74af95">FLOW_LOG_SET_CONTEXT</a></div><div class="ttdeci">#define FLOW_LOG_SET_CONTEXT(ARG_logger_ptr, ARG_component_payload)</div><div class="ttdoc">For the rest of the block within which this macro is instantiated, causes all FLOW_LOG_....</div><div class="ttdef"><b>Definition:</b> <a href="log_8hpp_source.html#l00405">log.hpp:405</a></div></div>
<div class="ttc" id="alog_8hpp_html_affcf2e4c496ce3f42adf981669c623b8"><div class="ttname"><a href="log_8hpp.html#affcf2e4c496ce3f42adf981669c623b8">FLOW_LOG_TRACE</a></div><div class="ttdeci">#define FLOW_LOG_TRACE(ARG_stream_fragment)</div><div class="ttdoc">Logs a TRACE message into flow::log::Logger *get_logger() with flow::log::Component get_log_component...</div><div class="ttdef"><b>Definition:</b> <a href="log_8hpp_source.html#l00227">log.hpp:227</a></div></div>
<div class="ttc" id="anamespaceflow_1_1async_html"><div class="ttname"><a href="namespaceflow_1_1async.html">flow::async</a></div><div class="ttdoc">Flow module containing tools enabling multi-threaded event loops operating under the asynchronous-tas...</div><div class="ttdef"><b>Definition:</b> <a href="async__fwd_8hpp_source.html#l00074">async_fwd.hpp:75</a></div></div>
<div class="ttc" id="anamespaceflow_1_1async_html_a0a06794b16b72f2829ce3353557c8485"><div class="ttname"><a href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485">flow::async::Synchronicity</a></div><div class="ttdeci">Synchronicity</div><div class="ttdoc">Enumeration indicating the manner in which asio_exec_ctx_post(), and various boost....</div><div class="ttdef"><b>Definition:</b> <a href="async__fwd_8hpp_source.html#l00222">async_fwd.hpp:223</a></div></div>
<div class="ttc" id="anamespaceflow_1_1async_html_a0a06794b16b72f2829ce3353557c8485a4d7a5700444c0570af37b1f9bcc6eb1f"><div class="ttname"><a href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485a4d7a5700444c0570af37b1f9bcc6eb1f">flow::async::Synchronicity::S_ASYNC</a></div><div class="ttdeci">@ S_ASYNC</div><div class="ttdoc">Simply post the given task to execute asynchronously in some execution context – as soon as the conte...</div></div>
<div class="ttc" id="anamespaceflow_1_1async_html_a0a06794b16b72f2829ce3353557c8485a57525f29ac96f4edd56c951e7d7c7b25"><div class="ttname"><a href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485a57525f29ac96f4edd56c951e7d7c7b25">flow::async::Synchronicity::S_ASYNC_AND_AWAIT_CONCURRENT_COMPLETION</a></div><div class="ttdeci">@ S_ASYNC_AND_AWAIT_CONCURRENT_COMPLETION</div><div class="ttdoc">Same as Synchronicity::S_ASYNC but the posting routine then waits as long as necessary for the given ...</div></div>
<div class="ttc" id="anamespaceflow_1_1async_html_a0a06794b16b72f2829ce3353557c8485ae9a9ae292ea3fbbe3b313348dcec0846"><div class="ttname"><a href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485ae9a9ae292ea3fbbe3b313348dcec0846">flow::async::Synchronicity::S_ASYNC_AND_AWAIT_CONCURRENT_START</a></div><div class="ttdeci">@ S_ASYNC_AND_AWAIT_CONCURRENT_START</div><div class="ttdoc">Same as Synchronicity::S_ASYNC but the posting routine then waits as long as necessary for the given ...</div></div>
<div class="ttc" id="anamespaceflow_1_1async_html_a0a06794b16b72f2829ce3353557c8485aff6bc53ee6c14f2eee463c06d9dff01f"><div class="ttname"><a href="namespaceflow_1_1async.html#a0a06794b16b72f2829ce3353557c8485aff6bc53ee6c14f2eee463c06d9dff01f">flow::async::Synchronicity::S_OPPORTUNISTIC_SYNC_ELSE_ASYNC</a></div><div class="ttdeci">@ S_OPPORTUNISTIC_SYNC_ELSE_ASYNC</div><div class="ttdoc">Execute the given task synchronously, if the scheduler determines that the calling thread is in its t...</div></div>
<div class="ttc" id="anamespaceflow_1_1async_html_a24567271e97a67d3cae6bd8bf8dc63c4"><div class="ttname"><a href="namespaceflow_1_1async.html#a24567271e97a67d3cae6bd8bf8dc63c4">flow::async::asio_exec_ctx_post</a></div><div class="ttdeci">void asio_exec_ctx_post(log::Logger *logger_ptr, Execution_context *exec_ctx, Synchronicity synchronicity, Task &amp;&amp;task)</div><div class="ttdoc">An extension of boost.asio's post() and dispatch() free function templates, this free function templa...</div><div class="ttdef"><b>Definition:</b> <a href="async_2util_8hpp_source.html#l00031">util.hpp:31</a></div></div>
<div class="ttc" id="anamespaceflow_1_1async_html_a4cce43f39672e80cba5512103c53ae60"><div class="ttname"><a href="namespaceflow_1_1async.html#a4cce43f39672e80cba5512103c53ae60">flow::async::cpu_idx</a></div><div class="ttdeci">uint16_t cpu_idx()</div><div class="ttdoc">Returns the 0-based processor logical (not hardware) core index of the core executing the calling thr...</div><div class="ttdef"><b>Definition:</b> <a href="async_8cpp_source.html#l00030">async.cpp:30</a></div></div>
<div class="ttc" id="anamespaceflow_1_1log_html_a5c602384e6fe9d7642740ac2fae4ad04"><div class="ttname"><a href="namespaceflow_1_1log.html#a5c602384e6fe9d7642740ac2fae4ad04">flow::log::Sev</a></div><div class="ttdeci">Sev</div><div class="ttdoc">Enumeration containing one of several message severity levels, ordered from highest to lowest.</div><div class="ttdef"><b>Definition:</b> <a href="log__fwd_8hpp_source.html#l00223">log_fwd.hpp:224</a></div></div>
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